A syringe for injection of fluid into the vitreous humor of an eye has a body that has, formed therein, an injection barrel and an extraction barrel, both of which have volumes that vary in response to movement of primary and secondary plungers that, are coupled to each other by a coupler. Two parallel needles, an extraction needle and an injection needle, emerge from the distal end of the body. Movement of the primary plunger injects fluid into the vitreous humor while at the same time causing the secondary plunger to extract the same volume of fluid from the vitreous humor, thus maintaining intraocular pressure.
